1. Field of the Invention
This invention relates generally to large-scale water treatment mixing apparatus""and more particularly to such apparatus""wherein the fluids being treated are forced to dissolve the highest possible level of oxygen possible.
2. Description of Related Art
The following art defines the present state of this field:
Rose et al., U.S. Pat. No. 2,784,150 describes a vacuum still capable of equilibrium evaporation with no bumping comprising a still pot having two necks, one of said necks being connected to a longitudinally extended tube closed at its far end, the second of said necks being connected to condensing means; the first of said necks and its attached tube having extending therein an agitator comprising an elongated shaft having disposed along its midsection in a spaced relationship a plurality of inverted cup-shaped baffles, each baffle having a plurality of perforation spacedly disposed over its surface, said shaft passing through the center of, and being rigidly attached to, each baffle, said shaft further having attached to its lower end an open-spiral elastic spring and to its upper end a totally enclosed chamber containing a soft iron core; the aforementioned tube attached to the first neck being surrounded near its upper end by a solenoid capable of imparting a vertically reciprocating motion to the enclosed agitator when said solenoid is cyclically activated and deactivated by passage of electric current therethrough.
Clough, Jr., U.S. Pat. No. 3,788,616, teaches a xe2x80x9csystem for simultaneously aerating and agitating a body of liquid. The system comprises a body that is pivotally mounted in the liquid with its pivot point located intermediate its ends, and means for feeding air to the lower side of the body. The body is adapted to trap alternately at each end sufficient air to cause that end to rise in the liquid, and means are provided for releasing the air trapped at each end of the body when that end has risen a predetermined amount, with the result that the body oscillates on its pivot axis in see-saw fashionxe2x80x9d.
Cruickshank et al., U.S. Pat. No. 3,773,015 describes valve arrangement used to control the release of air from the helmet of a miniature diver so as to cause the diver to periodically dive and ascend within an aquarium tank. The cycle period can be varied by controlling the rate at which air is supplied from a conventional aquarium air source. The diver is slidably mounted on a hollow tube for movement between first and second stations. At the first station, the tube has an opening to admit air to the interior of the diver to increase its buoyancy. The admitted air is retained in the diver until it reaches the second station. The tube has a necked down portion at the second station to release the air contained within the diver.
Everett, U.S. Pat. No. 4,363,212, teaches a xe2x80x9cbuoyancy prime mover that converts the potential energy of a gas buoyant within a liquid into rotating mechanical energy comprises a plurality of rigid or collapsible buckets joined by one or more chains with rotatable sprockets and shafts to form a continuous loop so that when the buoyant gas is trapped within the buckets, the buckets rise through the liquid and rotate the chain and sprockets to generate powerxe2x80x9d.
Parks, U.S. Pat. No. 4,595,296, teaches an invention which xe2x80x9crelates to a mixing and blending system in which pulsed air or gas bubbles of predetermined variable size and frequency are injected into a tank containing materials to be agitated or stirred for mixing or blending. The air introduced at the bottom of the tank through an air inlet opening. There may be more than one air inlet and the inlets may be provided with accumulator plates depending upon diameter and height of the tank in which the mixing and blending is taking place. The inlets are located so as to create circular torroidal flow of fluid in a generally vertical plane. The accumulator plate has the purpose of assisting the formation of essentially a single bubble from the compressed air charge made to the air inlet and increasing the time required for the bubble to rise through the liquid by causing it to be formed more quickly and closer to the bottom of the tank. Hence, the accumulator plate is utilized in low viscosity liquids such as waterxe2x80x9d.
Offermann, U.S. Pat. No. 4,737,036 describes a device for shipping cream or egg whites having a cup-shaped cylindrical housing with a performed bottom, a cap releasably locking the open top, a perforated plunger piston connected to one end of the piston rod and movable within the housing, the piston rod being movable through the cap and formed with a handle at its opposite end, one of two perforated plates spaced from the plunger piston on the piston rod. The perforated disc is biased by a spiral coil spring from the plunger and may be further biased from a second perforated disc. When the discs and plunger are compressed together, any product between them is squeezed out through their holes.
Hjort, et al, U.S. Pat. No. 4,779,990, teaches an xe2x80x9cimpeller apparatus for dispersing a gas into a liquid in a vessel includes a centrifugal flow turbine, the blades of which are formed with a substantially streamlined trailing surface terminated by a sharply pronounced spine. The blade is formed by a plate-like initial blank being cut to a shape having a central line of symmetry, the blank then being folded along the straight line of symmetryxe2x80x9d.
Litz, et al, U.S. Pat. No. 4,919,849, teaches a xe2x80x9cgas-liquid mixing process and apparatus having a vessel with an axial flow down-pumping impeller in a draft tube has gas ingestion tubes extending into a body of liquid from a hollow portion of the impeller shaft or other fluid communication means with the overhead gas in the vessel. Upon gas-liquid mixing at liquid levels that interfere with vortex development by the impeller, gas is drawn from the overhead through the ingestion tubes into the body of liquidxe2x80x9d.
Small, U.S. Pat. No. 5,156,788, teaches a xe2x80x9cdevice for use in the mixing of fluids, e.g. the gasification of liquids, comprises an elongate member including an internal passage; and, mounted on the elongate member via radial arms, one or more venturi members each having a convergent-divergent duct whose axis is substantially tangential to the elongate member, and in which the neck of the duct has an opening in communication, via passages in the radial, with the internal passage. On rotation of the device, reduced pressure in the duct neck draws fluid down the shaft of the elongate memberxe2x80x9d.
Middleton, et al, U.S. Pat. No. 5,198,156, teaches a turbine agitator assembly including a reservoir for liquid, a rotor mounted in the reservoir and with a plurality of radially extending blades, and sparger means for introducing a fluid into liquid in the reservoir. The fluid sparger means and the rotor are so constructed and arranged that, in use, the rotor blades (submerged in the liquid) and/or the liquid flow they generate disperse the sparged fluid. Each of the blades is hollow and has a discontinuous leading edge, only a single trailing edge along an acute angle, no external concave surface and an open radially outer end.
Stavropol Agric Ins, SU 1400651 describes a mixer comprising a cavity with a conical bottom equipped with a heater and mixing device. The latter is made in the form of a bell positioned in the cavity. The bell is equipped in the upper part with a by-pass valve, connected to the rod, whose length is greater than the bell height by a distance equal to total of the cone bottom height and valve slide valve run. A rigid net partition, separating the cavity from the gas carrier, is attached to the cavity cover. The bell floats up due to the buoyancy force, which occurs when the biogas accumulates under it. The valve strikes the partition and opens. When the biogas leaves from under the bell, it drowns and valve closes with the help of rod. Mixer is used for mixing liquid media applied in aerobic fermentation of livestock farming wastes. Its structure is simplified and power losses are decreased.
The prior art teaches the use of mixers similar in concept and construction to the present invention, but the prior art does not teach how to achieve the goals of the present invention. The present invention fulfills these needs and provides further related advantages as described in the following summary.
The present invention teaches certain benefits in construction and use, which give rise to the objectives described below.
Only three percent of the Earth""s water is potable. This small fraction has been dwindling over the course of recorded history due to natural and man-made effects. As human populations grow, a continuing problem worsens; the ability to obtain sufficient quantities of potable water for human use. The invention described herein is a partial solution to this problem. Sewage treatment is the primary means by which pollution of rivers, streams and lakes is prevented. Improvements in this area of industry are critical to the larger problem of providing fresh water supplies to the world""s population.
Gaseous oxygen has been used in activated sludge processing and aerobic digester sludge treatment facilities and processes. Common practice consists of maintaining dissolved oxygen quantities in the liquid media from zero to two parts per million by weight. The present invention uses a mixing method and use of oxygen, which enables the processing a significantly higher percent of sludge solids, by weight, than has been heretofore possible. Aerobic bacteria of various species are the means of processing sludge in digester tanks. The present invention uses a combination of improved mixing and a high dissolved oxygen content; between four and forty-five parts per million, to support a larger population density of aerobic bacteria for improved sludge processing in digester tanks. Such improvements relate to processing speed and quality as well. The apparatus uses bubbling diffusers populated in the tank bottom and sparger jets protruding from the walls of the tank. Both of these provide oxygen gas flows into the tank. The mass flow of this gas produces turbulence in the media providing high level contact between gas and liquid to maximize surface contact area. The present invention, a sludge digester, comprises a mixing tank providing an integral ceiling, interior wall surface and a floor surface. A vertical beam supports a mixing device engaged for movement along the vertical beam. A plurality of sparger jets protrudes from the wall surface for delivering an oxygen gas flow directly into the interior of the sludge. A second plurality of sparger jets terminates at the mixing tank floor surface for delivering oxygen gas into the mixing tank and a plurality of bubbling diffusers protrudes upwardly from the floor surface for delivering further oxygen gas flow into the mixing tank.
A primary objective of the present invention is to provide an apparatus and method of use of such apparatus that provides advantages not taught by the prior art. The invention uses high volume oxygen gas delivery and mechanical mixing to achieve significant improvements in the art.
Another objective is to provide such an invention capable of entraining gas into a process liquid at a very high rate.
A further objective is to provide such an invention capable of high rate mixing through gas injection turbulence.
A further objective is to provide such an invention capable of reducing harmful bacteria in downstream effluent to near zero.
A further objective is to provide such an invention capable of reducing sludge solids by up to 70% relative to conventional processing.
A further objective is to provide such an invention capable of improvements in sludge settling by up to 100%.
A further objective is to provide such an invention capable of high rate mixing through gas injection turbulence.
A still further objective is to provide a process method that is able to be completed as a continuous process within a field of industry where heretofore, such processing has been limited to batch process methods.
Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.